1. Field of the Invention
The present invention relates to an optical accessory adapter inserted between a lens apparatus and an optical accessory.
2. Description of the Related Art
Optical accessories (except for special-purpose accessories) to be attached to lens apparatuses are not built for the purpose of attachment to specific lens apparatuses, but optical accessories typically attached to lens apparatuses are built for general purpose.
In the case of ordinary lens apparatuses other than lens apparatuses used for the special purpose of magnifying imaging such as microscopes and macro lenses, imaging rays are divergent when seen in the direction from the frontmost lens toward the object. Therefore, optical accessories attached to such lens apparatuses on their object side have diameters equal to or larger than the attachment diameters of the lens apparatus.
Particularly in the case of lens apparatuses for wide angle imaging, the divergent angle of imaging rays is large. Therefore, in order to prevent interference of imaging rays and the lens barrel, the diameter of the front end portion of the lens barrel is enlarged, or the front end portion of the lens barrel is cut in a petal shape.
An optical accessory and an optical accessory adapter are disclosed, for example, in the U.S. Pat. No. 4,901,098. Specifically, this patent document discloses an optical accessory adapter constructed as an annular member (doughnut ring 100) having an aperture (varying aperture 112) allowing it to be attached to the lens apparatus. The optical accessory adapter is attached to a lens apparatus, and then a ring member (back ring 120) provided at the rear end of an optical accessory (matte box) is coupled to the annular member, whereby the lens apparatus, the adapter, and an optical accessory are coupled together.
THE MOTION PICTURE & TV ENGINEERING (No. 651, P. 51, November, 2006, Motion Picture and Television Engineering Society of Japan) discloses, in Picture 1 and FIG. 1 on page 51, an enlarged shape of the front end portion of a lens barrel. Japanese Patent Application Laid-Open No. 2005-4111 discloses a lens barrel cut in a petal shape.
In the case where the diameter of the front end portion of the lens barrel is enlarged as is the case with one disclosed in the aforementioned U.S. Pat. No. 4,901,098, if the diameter of the front end portion is matched with the attachment diameter of the optical accessory, an optical accessory adapter is not needed when using the optical accessory. However, this solution invites an increase in the outer diameter and an increase in the weight of the lens apparatus.
If an optical accessory is attached to a wide angle lens disclosed in Japanese Patent Application Laid-Open No. 2005-4111 using the optical accessory adapter disclosed in the aforementioned U.S. Pat. No. 4,901,098, there is a possibility that an inner part of the optical accessory adapter may extend inwardly beyond the cut portion of the lens barrel to interfere with imaging rays.
The interference of the optical accessory adapter and imaging rays can be prevented by shifting the position of the optical accessory adapter toward the image side. However, this may possibly prevent an appropriate space to be left between the optical accessory and the lens apparatus.
Referring, by way of example, to U.S. Pat. No. 4,901,098, a filter holding frame (filter holder body 140) disclosed in this patent document is inserted into the front end portion of the lens apparatus. Thus, as the optical accessory adapter enters from the front end of the lens apparatus toward the image side, the filter holding frame also comes closer to the lens apparatus, possibly leading to interference of the lens apparatus and the filter holding frame.